Devices, Systems and Methods of Informational Signal Synchronization Using a Reference Signal

The present application is a continuation of U.S. application Ser. No. 18/273,437 filed Jul. 20, 2023, which is a 371 of international application PCT/IB2022/050490, filed Jan. 20, 2022, which claims priority to U.S. provisional application No. 63/140,082, filed Jan. 21, 2021, the contents of which are incorporated by reference herein.

The specification relates generally to informational signal synchronization, and more particularly to devices, systems and methods of informational signal synchronization using a reference signal.

Many applications, such as condition assessment of pipes, may utilize the correlation of a signal received at two locations to estimate, for example, the position of a leak. The evolution of a known test signals between two measurement locations is of interest. Such systems require time-alignment or synchronization of the signals to be compared. Central processing may facilitate timing using a common clock or synchronization by means of a timing signal received from a satellite or atomic clock radio network, however this requires care to ensure that all signals and recordings are synchronized before and during the operation.

According to an aspect of the present specification, a method for signal synchronization is described. The method includes: recording, at a first sensor device, (i) a first informational signal as detected at the first sensor device; and (ii) a reference signal as detected at the first sensor device; recording, at a second sensor device (i) a second informational signal as detected at the second sensor device; and (ii) the reference signal as detected at the second sensor device; determining a time shift between the reference signal as recorded by the first sensor device and the reference signal as recorded by the second sensor device; and applying the determined time shift to the second informational signal to time-align the first informational signal and the second informational signal.

According to another aspect of the present specification, a computing device for signal synchronization is described. The computing device includes: a memory; a communications interface configured to communicate with a first sensor device and a second sensor device; a processor interconnected with the memory and the communications interface, the processor configured to: obtain, from the first sensor device, a first sensor recording, the first sensor recording including (i) a first data track representing a first informational signal as detected by the first sensor device and (ii) a first reference track representing a reference signal as detected by the first sensor device; obtain, from the second sensor device, a second sensor recording, the second sensor recording including (i) a second data track representing a second informational signal as detected by the second sensor device and (ii) a second reference track representing the reference signal as detected by the second sensor device; determine a time shift between the reference signal as recorded by the first sensor and the reference signal as recorded by the second sensor; and apply the determined time shift to the second informational signal to time-align the first informational signal and the second informational signal.

According to another aspect of the present specification, a sensor device for obtaining a sensor recording is described. The sensor device includes: an informational signal sensor configured to detect an informational signal; a reference signal sensor configured to detect a reference signal; a memory; and a processor interconnected with the informational signal sensor, the reference signal sensor and the memory, the processor configured to: generate informational data representing the informational signal and record the informational data in an informational track of a sensor recording; generate reference data representing the reference signal and record the reference data in a reference track of the sensor recording, wherein the informational track and the reference track are time-aligned relative to one another; and store the sensor recording locally in the memory.

Current methods of synchronization rely on the synchronization of all devices before and during recording operations, based on a common clock, or a timing signal received from a satellite or atomic clock radio network. Additionally, the measured signals are transmitted via a frequency modulated (FM) link to a base station to be processed with digital data acquisition and signal analysis. The operational limit of the instrument is therefore determined, in part, by the nominal range of the radio link. The radio links may also suffer from interference (which degrades signal quality) and have small dynamic range (implying that low level signals may not be detected).

For transducer separations greater than the range of the radio link, or where electromagnetic interference precludes the use of low-powered short-range radios, a different approach is utilized. It may be possible to use special signal cables to link sensors with a central data acquisition node. This involves the design, fabrication and testing of special signal buffer and line driver circuits that are needed to assure the noise and interference free signal transmission. Furthermore, it may not be possible to install the cables from a logistical point of view, or else installation would contribute a substantial material cost.

According to the present specification, a system for signal synchronization using a reference signal is described. The system utilizes sensor devices which may record both the informational signal (i.e., the signal of interest) as well as a reference signal, such as a broadcast of a frequency modulated (FM) radio station. Each sensor device may commence recording at approximately the same time but may differ by up to about a second based on the speed of transmission of an initiation signal (e.g., via cellular networks or other networks or manual application of inputs by multiple operators). That is, each sensor device may generate an independent sensor recording. After acquiring the requisite informational signal recordings, the sensor recordings may be provided to a centralized control device and synchronized using the reference signal after the recording operation is complete. Advantageously, varying types of reference signals may be used, including optical signals, if line-of-sight is available between the sensor devices, satellite radio, even random signals. Further, the number of simultaneous measurement points is not limited by radio transmitter capacity, and hence a measurement system employing multiple (e.g., 4, 6, 12, or more) sensor devices is possible for greater accuracy.

1 FIG. 100 100 102 102 1 102 2 102 1 102 2 102 102 104 102 106 depicts an example systemfor signal synchronization using a reference signal. The systemincludes a plurality of sensor devices, of which two sensor devices-and-are depicted (the sensor devices-and-are referred to herein generically as a sensor deviceand collectively as sensor devices) and a control devicein communication with the sensor devicesvia communication links.

102 102 102 108 112 102 110 114 102 The sensor devicesare generally configured to detect signals, such as optical signals, radio signals, acoustic signals, vibratory signals, displacement signals, temperature signals, pressure signals, voltages, current or the like. In particular, each sensor devicemay include one or more sensors, such as radio receivers or transceivers, microphones, optical detectors, accelerometers, temperature sensors, displacement sensors, pressure sensors, or other suitable sensors to detect said signals. More specifically, each sensor deviceis configured to detect an informational signal from an informational signal source, the informational signal received via an informational signal channel. Each sensor deviceis further configured to detect a reference signal from a reference signal source, the reference signal received via a reference signal channel. That is, the sensor deviceis configured to receive at least two signals (i.e., an informational signal and a reference signal) over different channels simultaneously.

102 1 108 112 1 110 114 1 102 2 108 112 2 110 114 2 For example, the first sensor device-is configured to detect a first informational signal from the informational signal sourcevia a first informational channel-and a reference signal from the reference signal sourcevia a first reference channel-. Similarly, the second sensor device-is configured to detect a second informational signal from the informational signal sourcevia the second informational channel-and the reference signal from the reference signal sourcevia the second reference channel-.

102 100 102 100 102 The internal components of the sensor devicesenabling such functionality will be described in greater detail below. In the present example, the systemincludes two sensor devices; in other examples, the systemmay include more than two sensor devices.

104 104 102 106 The control devicemay be a computing device such as a server, desktop computer, laptop computer, mobile device, such as a cell phone, a smart phone, a tablet, or the like. The control deviceis in communication with the sensor devicesvia communication links, such as wired or wireless links, or a combination of wired and wireless including direct links, or links that traverse one or more networks. For example, the communication links may utilize networks including any one of, or any combination of, a local area network (LAN) defined by one or more routers, switches, wireless access points or the like, any suitable wide area networks (WAN) including cellular networks and the internet, and the like.

104 102 102 102 104 104 102 102 The control deviceis generally configured to initiate and terminate recording operations at the sensor devices, and may further be configured to aggregate data from the sensor devicesand perform analysis on the signals recorded by the sensor devicesto time-align the informational signals. In some examples, the functionality described herein with respect to the control devicemay be implemented by one or more separate computing devices. For example, the control devicemay be configured to control the recording operations at the sensor devices, while a different computing device (not shown) may be configured to aggregate the data captured at the sensor devicesand analyze the data to time-align the informational signals.

108 102 108 102 108 102 The informational signal sourceis a source which emits informational signals for analysis. In particular, the informational signals are received and recorded at multiple locations (i.e., by the sensor devices) and may require time-alignment for relevant analysis. For example, the informational signal sourcemay be an acoustic source emitting an acoustic signal to be recorded at least two locations by the sensor devicesto determine properties of the medium through which the acoustic signal travelled. For example, an acoustic signal may be emitted into a pressure vessel to determine properties, such as wall thickness, faults, or other properties of the pressure vessel. The informational signal is not particularly limited to acoustic signals. In some examples, the informational signal sourcemay emit an electrical signal, a vibratory signal, a pressure signal, or the like, which is recorded by the sensor devices.

108 108 102 102 1 102 2 102 1 102 1 102 2 102 2 In some examples, the informational signal sourcemay emit an informational signal which may change over time and distance from the informational signal sourceto each of the sensor devices. Accordingly, the first informational signal may represent the informational signal as detected at the first sensor device-. Similarly, the second informational signal may represent the informational signal as detected at the second sensor device-. That is, given a single originating informational signal, the first sensor device-may capture first informational data representing the originating informational signal as detected at the first sensor device-and the second sensor device-may capture second informational data representing the originating informational signal as detected at the second sensor device-.

108 112 1 112 2 108 108 102 In other examples, the informational signal sourcemay emit multiple informational signals simultaneously via multiple informational channels, and hence the first informational signal and the second informational signal may be different signals sent via different informational channels (i.e., via the first informational channel-and the second informational channel-respectively). In still further examples, the informational signal sourcemay be implemented as multiple distinct signal sources. More generally, the informational signal sourcerepresents the source of multiple signals (i.e., as received by the sensor devices) which are to be time-aligned and analyzed and/or compared to extract some information.

110 100 102 110 110 102 110 102 110 The reference signal sourceis a source which emits at least one reference signal to assist with the signal synchronization operation of the system. In particular, the reference signal is a signal which may be broadcast over a wide range and is received substantially simultaneously and with substantially the same integrity and fidelity at each sensor device. That is, the reference signal sourceemits a reference signal which is consistently received irrespective of distance between the reference signal sourceand each sensor device. For example, the reference signal sourcemay be a frequency modulated (FM) radio station emitting FM radio waves as the reference signal. In other examples, where line of sight is available between the sensor devices, the reference signal sourcemay be a light source emitting an optical signal, such as a sequence of light pulses.

110 102 1 102 2 102 1 102 2 In particular, the reference signal sourceprovides a single reference signal which is consistently received, and hence the reference signal as detected by the first sensor device-and the reference signal as detected by the second sensor device-correspond to said single reference signal. That is, the first sensor device-may capture first reference data representing the reference signal, and the second sensor device-may capture second reference data representing the same reference signal.

110 100 100 100 110 As will be appreciated, the reference signal sourcemay be a component which is external to the system, but which provides a reference signal which may be utilized and recorded by the components of the system. In some examples, components of the systemmay use and record reference signals from two or more reference signal sources.

2 FIG. 102 1 104 Turning to, the first sensor device-, including certain internal components, and the control device, including certain internal components, are shown in greater detail.

102 1 200 204 208 212 216 102 2 102 The sensor device-includes a processor, a memory, an informational signal sensor, a reference signal sensor, and a communications interface. It will be understood that the second sensor device-and any further sensor devicesmay include similar components.

200 200 200 200 The processormay be a central processing unit (CPU), a microcontroller, a processing core, or similar. The processormay include multiple cooperating processors. In some examples, the functionality implemented by the processormay be implemented by one or more specially designed hardware and firmware components, such as a field-programmable gate array (FPGA), an application-specific integrated circuit (ASIC) and the like. In some examples, the processormay be a special purpose processor which may be implemented via dedicated logic circuitry of an ASIC, an FPGA, or the like in order to enhance the processing speed of the signal recording operation discussed herein.

200 204 204 200 204 204 200 204 200 204 220 200 200 102 1 100 220 204 224 102 1 204 224 102 1 100 The processoris interconnected with a non-transitory computer-readable storage medium, such as the memory. The memorymay include a combination of volatile memory (e.g., random access memory or RAM) and non-volatile memory (e.g., read only memory or ROM, electrically erasable programmable read only memory or EEPROM, flash memory). The processorand the memorymay comprise one or more integrated circuits. Some or all of the memorymay be integrated with the processor. The memorystores computer-readable instructions for execution by the processor. In particular, the memorystores a control applicationwhich, when executed by the processor, configures the processorto perform various functions discussed below in greater detail and related to a signal recording operation of the sensor device-for a signal synchronization operation of the system. In other examples, the applicationmay also be implemented as a suite of distinct applications. The memorymay also store a repositoryconfigured to store sensor recordings from recording operations of the sensor device-. In other examples, the memoryand/or the repositorymay also store other rules and data pertaining to the signal recording operation of the sensor device-and the signal synchronization operation of the system.

102 1 208 108 208 208 208 102 1 The sensor device-also includes the informational signal sensorconfigured to detect an informational signal emitted from the informational signal source. For example, the informational signal sensormay be a radio transceiver, a photodetector, an accelerometer, a temperature sensor, a pressure sensor, a displacement sensor, combinations of the above, and the like. In some examples, the informational signal sensormay include a suite of sensors configured to detect multiple informational signals or multiple types of informational signals. In particular, the specific components of the informational signal sensorare selected based on the type of informational signal the sensor device-is to detect.

102 1 212 110 212 212 102 1 The sensor device-further includes the reference signal sensorconfigured to detect the reference signal emitted from the reference signal source. For example, the reference signal sensormay be a radio receiver/antenna, a photodetector, combinations of the above, and/or other suitable sensors capable of detecting the reference signal. In particular, the specific components of the reference signal sensorare selected based on the type of reference signal the sensor device-is to detect.

208 212 104 208 212 208 212 104 208 212 104 104 208 212 208 212 208 212 104 104 104 104 104 104 The reference signal (e.g. the FM frequency) may be pre-selected or it may be selected by the according to the signal strength measured by the reference signal sensors,at the first and second locations. Before receiving the initiation signal at the control device, one or both of the reference signal sensors,may measure the signal strength of at least one reference signal. The reference signal sensors,may select the reference signal with the highest signal strength at the respective location, or the selection may be made by the control device. In implementations where the reference signal sensors,select the reference signal, the selection may be overridden by the control deviceif the first and second reference sensors do not select the same reference signal. In some implementations, if the signal strength of a first reference signal is below a pre-determined threshold at either location, control devicemay control the reference signal sensors,to measure the signal strength of a second reference signal until the sensors,detect a reference signal that meets the pre-determined threshold at both locations. In other implementations, the reference signal sensors,may measure the signal strength of two or more reference signals, and the control devicemay select the reference signal with the highest combined signal at both locations. For example, the control devicemay select the reference signal with the highest signal strength at the first location and the third highest signal strength at the second location. The control devicemay be programmed to select a reference signal, or the control devicemay select a reference signal based on an input by the operator at the control device. In some examples, the operator may override any selection made by the control device.

102 1 216 200 216 102 1 104 216 106 102 1 The sensor device-also includes the communications interfaceinterconnected with the processor. The communications interfaceincludes suitable hardware (e.g., transmitters, receivers, network interface controllers and the like) allowing the sensor device-to communicate with other computing devices, in particular, with the control device. The specific components of the communications interfaceare selected based on the type of network or other links, including the communication linksthat the sensor device-is to communicate over.

102 1 200 In some examples, the sensor device-may also include one or more input and/or output devices (not shown), interconnected with the processor. The input devices can include one or more buttons, keypads, dials, touch-sensitive display screens or the like for receiving input from an operator, for example, to configure the FM radio settings when the reference signal to be used is an FM radio station. The output devices can include one or more display screens, sound generators, vibrators or the like for providing output or feedback to an operator.

104 250 254 258 The control deviceincludes a processor, a memory, and a communications interface.

250 250 250 250 The processormay be a CPU, a microcontroller, a processing core, or similar. The processormay include multiple cooperating processors. In some examples, the functionality implemented by the processormay be implemented by one or more specially designed hardware and firmware components, such as an FPGA, an ASIC and the like. In some examples, the processormay be a special purpose processor which may be implemented via dedicated logic circuitry of an ASIC, an FPGA, or the like in order to enhance the processing speed of the signal synchronization operation discussed herein.

250 254 254 250 254 254 250 254 250 254 262 250 250 100 262 204 266 204 266 100 The processoris interconnected with a non-transitory computer-readable storage medium, such as the memory. The memorymay include a combination of volatile memory (e.g., random access memory or RAM) and non-volatile memory (e.g., read only memory or ROM, electrically erasable programmable read only memory or EEPROM, flash memory). The processorand the memorymay comprise one or more integrated circuits. Some or all of the memorymay be integrated with the processor. The memorystores computer-readable instructions for execution by the processor. In particular, the memorystores a control applicationwhich, when executed by the processor, configures the processorto perform various functions discussed below in greater detail and related to a signal synchronization operation of the system. In other examples, the applicationmay also be implemented as a suite of distinct applications. The memorymay also store a repositoryconfigured to store time-aligned informational signals. In other examples, the memoryand/or the repositorymay also store other rules and data pertaining to the signal synchronization operation of the system.

104 258 250 258 104 102 258 106 104 The control devicealso includes the communications interfaceinterconnected with the processor. The communications interfaceincludes suitable hardware (e.g., transmitters, receivers, network interface controllers and the like) allowing the control deviceto communicate with other computing devices, in particular, with the sensor devices. The specific components of the communications interfaceare selected based on the type of network or other links, including the communication linksthat the control deviceis to communicate over.

104 250 102 In some examples, the control devicemay also include one or more input and/or output devices (not shown), interconnected with the processor. The input devices can include one or more buttons, keypads, dials, touch-sensitive display screens or the like for receiving input from an operator, for example, to initiate a recording operation at the sensor devices. The output devices can include one or more display screens, sound generators, vibrators or the like for providing output or feedback to an operator.

100 300 100 300 220 262 200 250 300 3 FIG. 3 FIG. 1 2 FIGS.and The operation of the systemwill now be described in greater detail, with reference to.depicts a flowchart of an example methodof signal synchronization using a reference signal, which will be described in conjunction with its performance in the system, with reference to the components illustrated in. In particular, the methodmay be implemented via execution of the applicationsandby the processorsand, respectively. In other examples, the methodmay be performed by other suitable computing devices or in other suitable systems.

305 102 1 102 1 102 1 102 1 104 400 102 400 102 1 400 102 2 4 FIG. At block, the first sensor device-records a first informational signal as detected at the first sensor device-and the reference signal as detected at the first sensor device-. The first sensor device-may initiate the recording in response to an initiation signal, received for example from the control device. For example, referring to, an example methodof performing a recording operation at a sensor deviceis depicted. The methodwill be described in conjunction with its performance by the first sensor device-; in other examples, the methodmay be performed by other suitable devices, such as the second sensor device-.

405 102 1 104 102 1 104 102 2 102 1 102 1 102 At block, the sensor device-receives an initiation signal. For example, the initiation signal may be sent from the control device. The initiation signal may be received, for example via a mobile network, an internet connection, or the like. In other examples, the initiation signal may be an input from an operator of the sensor device-. For example, the operator may be utilizing another computing device (e.g., a mobile phone) to receive start instructions from an operator of the control device(or otherwise central controller) or an operator of the second sensor device-, and the operator may manually provide the input to the sensor device-to act as an initiation signal to initiate the recording operation at the sensor device-. It is not necessary for the initiation signal to be received at the first and second sensor devicesat precisely the same time.

410 102 1 102 1 208 212 108 110 102 1 208 212 At block, in response to the initiation signal, the sensor device-initiates the recording operation. In particular, the sensor device-may initialize the informational signal sensorand the reference signal sensorto enable them to detect informational signals emitted from the informational signal sourceand reference signals emitted from the reference signal source, respectively. The sensor device-further initiates a first sensor recording to record the signals detected by the informational signal sensorand the reference signal sensor.

102 1 108 208 102 1 102 1 102 1 102 1 102 1 In particular, the first sensor device-detects an informational signal emitted from the informational signal sourcevia the informational signal sensor. In response to detecting the informational signal, the first sensor device-generates first informational data representing the informational signal as detected at the first sensor device-. That is, the first informational signal corresponds to the first informational data representing the informational signal as detected at the first sensor device-. The first sensor device-may record the first informational data in a first informational track of the first sensor recording. Thus, the first informational track represents the first informational signal as detected at the first sensor device-.

102 1 110 212 102 1 102 1 102 1 102 1 The first sensor device-further detects a reference signal emitted from the reference signal sourcevia the reference signal sensor. In response to detecting the reference signal, the first sensor device-generates first reference data representing the reference signal as detected at the first sensor device-. The first sensor device-may record the first reference data in a first reference track of the first sensor recording. Thus, the first reference track represents the reference signal as detected at the first sensor device-.

102 1 The informational and reference tracks of the sensor recording are correlated to each other to be time-aligned relative to one another. For example, they may begin at the same time. In other examples, they may be recorded relative to an internal clock of the sensor device-.

415 102 1 104 102 1 At block, the sensor device-receives a stop or termination signal. For example, the stop signal may be sent from the control device. The stop signal may be received, for example via a mobile network, an internet connection, or the like. In other examples, the stop signal may also be a manual input from an operator of the sensor device-.

420 102 1 102 1 208 212 102 1 208 212 208 212 102 1 At block, in response to the stop or termination signal, the sensor device-stops the recording operation. In particular, the sensor device-may deactivate the informational signal sensorand the reference signal sensor. In other examples, the sensor device-may leave the informational signal sensorand the reference signal sensoractive but may stop recording the informational signal and the reference signal detected at the informational signal sensorand the reference signal sensoractive respectively. That is, the sensor device-ends the recording of the first informational data and the first reference data on the first informational and first reference tracks of the first sensor recording, respectively.

425 102 1 102 1 102 1 224 102 1 At block, the sensor device-stores the first sensor recording locally on the sensor device-. For example, the sensor device-may store the first sensor recording in the repository. The first sensor recording may be stored in association with identification data or other parameters of the recording, such as a time of the recording (e.g., a start time, end time, duration, as determined based on an on-board clock), an identifier of the recording and/or the sensor device-, or other suitable and pertinent data.

3 FIG. 310 102 2 102 2 102 1 102 2 104 102 2 400 102 2 108 102 1 102 2 102 2 102 2 102 2 Returning to, at block, the second sensor device-records a second informational signal as detected at the second sensor device-and the reference signal as detected at the second sensor device-. The second sensor device-may similarly initiate the recording in response to an initiation signal, received for example from the control device. For example, the second sensor device-may execute the methodto generate a second sensor recording. In particular, the second sensor device-detects an informational signal emitted from the informational signal source. The informational signal may the same one as the one detected at the first sensor device-or it may be a different informational signal. In response to detecting the informational signal, the second sensor device-generates second informational data representing the informational signal as detected at the second sensor device-. That is, the second informational signal corresponds to the second informational data representing the informational signal as detected at the second sensor device-. The second sensor device-may record the second informational data in a second informational track of the second sensor recording.

102 2 110 102 2 102 2 102 2 102 2 The second sensor device-further detects the reference signal emitted from the reference signal source. In response to detecting the reference signal, the second sensor device-generates second reference data representing the reference signal as detected at the second sensor device-. The second sensor device-may record the second reference data in the second reference track of the second sensor recording. Thus, the second reference track represents the reference signal as detected at the second sensor device-.

The tracks of the sensor recording are similarly correlated to each other to be time-aligned relative to one another.

102 102 102 The sensor devicesare not limited to detecting a single reference signal. In some examples, the sensor devicehas more than one channel for detecting more than one reference signal. Sensor devicesmay detect multiple reference signals simultaneously or sequentially.

315 104 305 310 104 104 102 1 102 2 At block, the control deviceobtains the first sensor recording generated at blockand the second sensor recording generated at blockfor analysis. In particular, after obtaining the sensor recordings, the control devicedetermines a time shift between the first reference track and the second reference track. That is, the control devicedetermines a time shift between the reference signal as recorded by the first sensor device-and the reference signal as recorded by the second sensor device-.

104 102 1 102 2 For example, the control devicemay determine the time shift by cross-correlating the reference signal as recorded by the first sensor device-and the reference signal as recorded by the second sensor device-, determining a peak of the cross-correlation and defining a time associated with the peak as the time shift.

5 FIG.A 5 FIG.B 500 502 504 500 504 504 506 315 300 104 For example, referring to, example reference track recordingsandrecorded by two separate sensor devices are depicted.depicts a cross-correlationof the reference track recordingsand. As can be seen, the cross-correlationhas a peakat about 0.4798 seconds. Thus, at blockof the method, the control devicemay determine the time shift to be about 0.4798 seconds.

3 FIG. 320 104 315 104 104 Returning to, at block, the control deviceapplies the time shift determined at blockto the informational signals time-align the informational signals. Specifically, the control devicemay apply the determined time shift to the second informational signal to time-align the first informational signal and the second informational signal. That is, the control devicemay shift the informational signals relative to each other, by the determined time shift such that the cross-correlation of the informational signals has a global maximum (i.e., a peak) at zero-time delay.

104 In some examples, after applying the time shift to the second informational signal, the control devicemay conduct a quality check of the first and second informational signals. The quality check may include computing coherence, computing the signal-to-noise ratio, identifying contamination to the signal, combinations thereof, and the like. For example, the signal may be contaminated by electromagnetic interference which can be detected near an electrical station. The quality check may identify contamination caused by said electrical station.

104 104 102 s s When computing coherence, the control devicemay apply a further cross-correlation function to verify that the peak is at approximately zero-time delay. Specifically, the control devicemay compute the coherence of the first and second informational signals to verify that the informational signals are synchronized. In one example, the pre-determined threshold for coherence is an error of about ±0.5/f, where fis the sampling frequency of sensor devices.

104 100 305 320 104 100 305 320 104 104 305 320 100 If the coherence is below a pre-determined threshold, the control devicemay control the systemto repeat stepsto. Similarly, if the signal-to-noise ratio fails to meet a pre-determined threshold or contamination exceeds a pre-determined threshold, the control devicemay control the systemto repeat the stepto. The quality check may be performed by the control deviceat the site of the synchronization, which can provide confirmation of the quality of the data shortly after the signals are recorded. This allows the control deviceto identify a problem with the data and repeat the stepstobefore the systemis disassembled or users return to a base station.

102 104 104 In implementations where the sensor devicesrecord two or more reference signals, the control devicemay perform a quality check to compare the two or more reference signals. As part of the quality check, the control devicemay select the optimal reference signal from the two or more reference signals. The optimal reference signal may be selected as the reference signal with the highest coherence, the lowest signal-to-noise ratio, the least signal contamination, or a combination thereof.

325 104 104 104 104 266 102 1 102 2 At block, the control deviceoutputs the time-aligned informational signals for further processing. In some examples, the control devicemay perform the additional processing, while in other examples, the control devicemay communicate the time-aligned informational signals to a separate computing device (e.g., a server, a desktop or laptop computer) or to a storage medium such as a universal serial bus (USB) stick for transfer to another computing device, or the like. In still further examples, the control devicemay simply store the time-aligned informational signals in the repository. For example, the time-aligned informational signals may be used to determine properties of a target object based on the difference in propagation of the informational signal over time to the first sensor device-at a first location and to the second sensor device-at a second location.

6 FIG. 100 600 600 104 608 102 1 102 2 For example, referring to, an example application of the above-described signal synchronization systemto an example systemfor non-invasive determination of target properties of a pressure vessel is depicted. The systemincludes the control device, a signal generator, and the sensor devices-and-.

600 601 601 602 600 602 602 602 600 601 608 102 603 602 600 The systemis deployed to determine properties of a pressure vessel. For example, the pressure vesselmay be a pipe defined by a wallenclosing a fluid. The systemmay determine properties of the wall, such as a thickness of the wallat various points along the wall, locations of any cracks or faults of the wall, and the like. More particularly, the systemis configured to determine the properties of the pressure vesselusing non-invasive methods. Accordingly, the signal generatorand the sensorsare deployed at an external surfaceof the wall. The systemmay thus be employed on in-use pressure vessels without destroying or otherwise affecting the integrity of the pressure vessel.

608 108 100 608 601 608 601 603 608 601 601 608 608 608 608 104 616 608 104 The signal generatoracts as the informational signal sourceof the system. In particular, the signal generatoris physically, thermally, vibrationally, electrically or acoustically coupled to a fluid contained within the pressure vessel. The signal generatoris disposed externally to the pressure vessel, such as at the external surface, at fittings, flanges, valves, or the like. The signal generatoris configured to emit signals into the pressure vessel, and more particularly into the fluid contained in the pressure vessel. Subsequent examples describe the signal generatoras emitting an acoustic signal, however it should be understood that the signal generatoris not particularly limited. Signals emitted by the signal generatormay include electrical signals, acoustic signals, vibratory signals, pressure signals, combinations thereof and the like. The signal generatormay be in communication with the control devicevia communication link, over which the signal generatormay receive instructions from the control device.

102 601 102 608 601 608 102 100 100 608 The sensorsare also physically, thermally, vibrationally, electrically or acoustically coupled to the fluid and disposed externally to the pressure vesselto detect signals. In particular, the sensorsmay employ accelerometers, temperature sensors, pressure sensors, displacement sensors, electrical sensors, combinations of the above, and the like to detect signals emitted by the signal generator, as transmitted or reflected through the pressure vessel. In some examples, the signal generatoremits an acoustic signal which is detected by the sensor with at least one of: a pressure sensor and a temperature sensor. The sensorsmay further employ accelerometers, temperature sensors, pressure sensors, displacement sensors, electrical sensors, combinations of the above, and the like to detect background conditions or characteristics of the system. Sensor data pertaining to background conditions or characteristics of the systemmay aid or enhance the interpretation of informational signals emitted by the signal generator.

102 610 610 110 100 The sensorsare further in communication with a radio towerto detect FM radio waves as the reference signal. That is, the radio toweracts as the reference signal sourceof the system.

102 102 104 608 102 608 601 104 608 102 601 104 601 601 601 104 102 102 102 102 In operation, prior to initiating recordings, an operator may tune the radio receiver of the sensor devicesto the same radio station (e.g., a pre-selected radio station). When the sensor devicesare tuned, the control devicemay issue an initiation signal to the signal generatorand the sensor devices. In response to an initiation signal, the signal generatoremits acoustic signals into the pressure vessel. In particular, the control devicemay select a particular frequency and duration at which the signal generatoris to emit the acoustic signals to optimize the signals received at the sensor devicesand to optimize the determination of the target properties of the pressure vessel. The frequency and duration of the acoustic signals may be selected according to a predefined program stored in memory at the control deviceor may be dynamically selected based on the calibration results and previously emitted and detected acoustic signals. For example, the frequency and duration may be selected based on one or more of: the material of the pressure vessel, the diameter of the pressure vessel, the type of fluid contained in structures of the pressure vessel. For example, the control devicemay control the frequency, duration, and power of the emitted acoustic signals to optimize the signals received at the sensor devices. The acoustic signals may be emitted at frequencies in the range of 1 to 20,000 Hz. In some examples, the acoustic signals may be emitted at higher frequencies. Additionally in response to the initiation signal, the sensor devicesinitiate recording operations, to generate sensor recordings, each having an informational track storing the acoustic signals as detected at the respective sensor device, and a reference track storing the FM radio signal as detected at the respective sensor device.

104 608 102 The control devicemay optionally issue a stop or termination signal to cause the signal generatorto stop issuing acoustic signals, and to stop the sensor recordings at the sensor devices.

104 102 601 102 102 601 102 Subsequently, the control device(or another computing device, as appropriate), may obtain the sensor recordings from the sensor devices. In order to determine properties of the pressure vessel, the acoustic signals as received at the sensor devicesare cross-correlated and compared; the differences in travel time and signal strength between the signals as received at each of the sensor devicesprovides insight as to the properties of the pressure vessel. However, in order to determine accurate differences in travel time, the acoustic signals as received at each of the sensor devicesshould be time-aligned.

104 601 601 104 Accordingly, the control devicemay proceed to determine the time shift between the reference signal tracks and apply the time shift to the informational (acoustic) signals to time-align the detected acoustic signals. The time-aligned detected acoustic signals may then be cross-correlated and compared to accurately determine properties of the pressure vessel. For example, the properties may be determined by methods described in U.S. Provisional Application No. 63/023,017, the contents of which are incorporated by reference. That is, the properties of the pressure vesselmay be determined based on the first informational signal and the second informational signal, as time-aligned by the control device.

As described above, a system for signal synchronization is provided. The system includes sensor devices which are capable of recording an informational signal (i.e., a signal of interest) on a first track and a reference signal (i.e., which is consistently and universally broadcasted to all sensor devices) on a second track. A control device may subsequently use the reference signals to determine a time shift between the recordings, and apply the time shift to the informational signals to time-align the informational signals. Advantageously, the time-alignment or synchronization of the signals may be performed after the recording operation, rather than requiring synchronization before and during the recording operation. Further, since the sensor recordings are stored locally, the present system provides greater flexibility in the physical range (i.e., distance) and number of sensor devices for which signal synchronization is to be performed.

The scope of the claims should not be limited by the embodiments set forth in the above examples but should be given the broadest interpretation consistent with the description as a whole.